Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $218.60   12.119%   $245.0921   $245.09   $245.10   $245.10  
  Purchase #2 $207.97   5.160%   $218.7013   $218.70   $218.70   $218.70  
  Purchase #3 $173.74   3.194%   $179.2893   $179.29   $179.30   $179.30  
  Purchase #4 $121.66   10.307%   $134.1995   $134.20   $134.20   $134.20  
  Purchase #5 $220.46   6.280%   $234.3049   $234.30   $234.30   $234.30  
  Purchase #6 $21.85   6.809%   $23.3378   $23.34   $23.35   $23.30  
  Purchase #7 $111.26   8.497%   $120.7138   $120.71   $120.70   $120.70  
  7 purchase totals = $1,075.54       $1,155.6387   $1,155.63   $1,155.65   $1,155.60